1. Field of the Invention
This invention relates to a method of generating an information signal to be recorded, a method of reproducing an information signal, a method of transmitting an information signal, an apparatus for generating an information signal to be recorded, an apparatus for reproducing an information signal, an apparatus for transmitting an information signal, an information-signal recording medium, and a computer program for transmitting an information signal.
2. Description of the Related Art
In some cases, an analog audio signal and an analog video signal accompanied with the analog audio signal are converted into a digital audio signal and a digital video signal before being transmitted or recorded on a recording medium. The conversion of the analog video signal into the digital video signal is based on, for example, a compressively encoding procedure. A temporal error tends to occur between the digital audio signal and the digital video signal.
According to a known system designed to compensate for such a temporal error between audio and video, first timing information relating to desired audio playback moments is added to a digital audio signal while second timing information relating to desired video playback moments is added to a digital video signal. The desired audio playback moments and the desired video playback moments are chosen to provide synchronization between audio and video. During playback, information represented by the digital audio signal is converted into sound at a timing decided by the first timing information while information represented by the digital video signal is indicated at a timing decided by the second timing information. As a result, the playback of audio and the playback of video are synchronized with each other.
In a known multiplexing-based transmitting or recording system, a portion of a digital audio signal and a portion of a digital video signal which relate to a same desired playback moment are transmitted or recorded while being placed in a same group through a multiplexing procedure. This design makes possible the synchronous playback of audio and video.
Recently, multiplexed data containing compressively-encoded video data and audio data have sometimes been handled as a form of a bit stream which is referred to as a transport stream or a program stream, and which is designed to make possible the synchronous playback of audio and video. Generally, it is not easy to edit only audio data in such multiplexed data.
An example of the editing is post-recording or after-recording which edits only audio data in multiplexed data (a bit stream) and replaces the audio data with new data. The post-recording (the after-recording) is complicated.
Japanese patent application publication number 6-275018/1994 discloses a recording and reproducing apparatus which operates in either a recording mode or a reproducing mode.
During the recording mode of operation of the apparatus in Japanese application 6-275018, information signals from N sources are converted into first digital signals through a compressively encoding procedure, and the first digital signals are modulated and converted into second digital signals. The second digital signals are written into a recording medium on a time sharing basis. During the reproducing mode of operation, the second digital signals are read out from the recording medium on a time sharing basis, and the read-out second digital signals are demodulated and converted back into the reproduced first digital signals. The reproduced first digital signals are converted back into the reproduced information signals. The reproduced information signals are simultaneously outputted.
Japanese patent application publication number 11-144378/1999 discloses a method of after-recording (post-recording) in which original data including a video bit stream are read out from a digital recording medium. The read-out original data are decoded. Audio data are encoded into a new audio bit stream in synchronism with the decoding of the original data. The new audio bit stream is written into an area of the digital recording medium which approximately corresponds in time position to the original-data recording area.
Japanese patent application publication number P2000-197005A discloses an information recording medium having an area “A” and an area “B”. The area “A” stores a stream of packs including video packs and audio packs. The area “B” stores a table having first, second, and third information pieces. By referring to the first information piece in the table, a decision is made as to whether or not audio data in the audio packs in the area “A” correspond to silence. In the case where the audio data in the audio packs correspond to silence, post-recording (after-recording) can be implemented as follows. By referring to the second and third information pieces in the table, a new audio signal is encoded into new audio data, and the new audio data are formatted into new audio packs. The new audio packs are written over the old audio packs in the area “A”.
Prior-art post-recording (prior-art after-recording) writes new audio data into an original multiplexed main stream so that the original multiplexed main stream changes to new one. Generally, it is difficult to convert the new multiplexed main stream back into the original one.
In the prior art, it is difficult to post-record a plurality of new audio signals, and to select one from the new audio signals during playback.